Rescuing 3T3-L1 adipocytes from insulin resistance induced by stimulation of Akt-mammalian target of rapamycin/p70 S6 kinase (S6K1) pathway and serine phosphorylation of insulin receptor substrate-1: effect of reduced expression of p85alpha subunit of phosphatidylinositol 3-kinase and S6K1 kinase.
Phosphorylation of insulin receptor substrate-1 (IRS-1) on serine residues has been recognized as a mechanism responsible for a diminution of insulin action and insulin resistance. Potential approaches to improve insulin sensitivity may include interference with and/or reduction in expression of certain signaling intermediates that participate in the pathogenesis of insulin resistance. In this study, we transduced fully differentiated 3T3-L1 adipocytes with a constitutively active myristoylated Akt that led to hyperactivation of mammalian target of rapamycin and p70 S6 kinase (S6K1), increased serine phosphorylation of IRS-1, and reduction in insulin-stimulated phosphatidylinositol (PI) 3-kinase activity and glucose transport. We then reduced expression of the PI 3-kinase regulatory subunit, p85alpha, or expression of S6K1 kinase using small interfering RNA transfections, which led to a reduction in p85alpha expression of 70% at 48 h (P < 0.05) and S6K1 of 49% (P < 0.05). Reduction in expression of either p85alpha or S6K1 achieved with small interfering RNA in the presence of myristoylated Akt rescued 3T3-L1 adipocytes from the insulin resistance induced by serine phosphorylation of IRS-1 and completely restored insulin-stimulated activation of PI 3-kinase and glucose uptake. We conclude that reduction in expression of p85alpha or S6K1 could represent therapeutic targets to mitigate insulin resistance.
Adochio
Rebecca
R
Department of Veterans Affairs, University of Colorado Denver, Aurora, Colorado 80045, USA.
Leitner
J Wayne
JW
Hedlund
Reed
R
Draznin
Boris
B
D041721:3T3-L1 Cells; D017667:Adipocytes / Q000187:drug effects / Q000378:metabolism* / Q000473:pathology; D000818:Animals; D015316:Genetic Therapy / Q000379:methods; D055504:Insulin Receptor Substrate Proteins / Q000378:metabolism*; D007333:Insulin Resistance / Q000235:genetics / Q000502:physiology; D051379:Mice; D051058:Oncogene Protein v-akt / Q000235:genetics / Q000378:metabolism; D019869:Phosphatidylinositol 3-Kinases / Q000378:metabolism* / Q000502:physiology; D000081082:Phosphoinositide-3 Kinase Inhibitors; D010766:Phosphorylation / Q000235:genetics; D011494:Protein Kinases / Q000378:metabolism*; D021122:Protein Subunits / Q000378:metabolism / Q000502:physiology; D034741:RNA, Small Interfering / Q000494:pharmacology; D038744:Ribosomal Protein S6 Kinases, 90-kDa / Q000037:antagonists & inhibitors / Q000378:metabolism*; D012694:Serine / Q000378:metabolism; D015398:Signal Transduction / Q000235:genetics; D058570:TOR Serine-Threonine Kinases; D014162:Transfection
D055504:Insulin Receptor Substrate Proteins; D051058:Oncogene Protein v-akt; D019869:Phosphatidylinositol 3-Kinases; D000081082:Phosphoinositide-3 Kinase Inhibitors; D011494:Protein Kinases; D021122:Protein Subunits; D034741:RNA, Small Interfering; D038744:Ribosomal Protein S6 Kinases, 90-kDa; D012694:Serine; D058570:TOR Serine-Threonine Kinases; C526295:Irs1 protein, mouse; C546843:mTOR protein, mouse; C512964:Rps6ka1 protein, mouse